The present invention relates to a video printer for printing video signals, and in particular to a control circuit for thermal printer.
In a printer of the prior art as described in JP-A-61-135768, data of one line are held once in a line buffer and then transferred to a shift register having bits respectively connected to heating elements of a thermal head via latches, flip-flops and switches, thus printing being performed. In case gradation recording is performed by using a printer of the prior art, graded data are stored beforehand in a ROM to control the conduction time of the thermal head as described in JP-A-55-69482.
If graded recording is attempted by using a printer of the prior art, comparison means must be provided for each dot of the thermal head as described in JP-A-55-69482, resulting in a problem of increased circuit size.
If gradation data are stored in a line buffer in order to prevent the increase in circuit size and the output of the line buffer is compared with the output of the gradation counter to write the comparison output into a shift register, there is a fear that data write time into the shift register might hinder the high speed printing.